I'm entertaining the idea of porting the heads from the doner car, and swaping them onto the engine in my monte once I finalize the trans swap. I wanted to know how much to port the heads. The intake side seems easy enough, just gasket match it. But the exhaust ports are way smaller than the ports on the manifold, and even smaller when you compare them to the 1.61" inner diameter pipe that I'll be using to make the custom turbo mainifolds. I know that the more I open up those ports supposedly the less exhaust gas velocity I'll have. But how would the amount of gas and velocity be affected by adding the turbo?

 

Have you read a book on head porting yet? If not, I'd pick one up first. Wont have anything 3800 specific, but itll at least give you the theory to understand what's going on as it's fairly complicated.

IMO for a first time doing home porting, I'd suggest staying on the more conservative end and not making any major geometry changes, but more doing an advanced cleanup of typical factory issues. You dont have a flow bench to measure actual results, and it's very possible to make heads flow worse at the lifts you'll be seeing, so you dont want to get too crazy. Youd rather go easy and get half the gains of real shop ported heads than swing for the fences and end up with trash.

I know you mention the inlet / outlet sizes specifically, but IMO that's not where your focus should be. For 2 reasons:
1.) Changes only to the inlet / outlet dont have a big gain on flow elsewhere. You cant carry the large port size down into the port or you'll blow through the wall. For the exhaust port, I liken it to expanding the last inch of your exhaust tailpipe from 2" diameter to 3". Its not going to flow more overall just because the tail end of it is bigger.
2.) Those sizes / shapes are specifically engineered and cast that way. If there was a notable improvement with a different size / shape, they would've been cast like that instead. Its further evidenced by aftermarket ported 3800 heads. They maintain the general shape of the exhaust port and dont open it much - they keep a pretty substantial reversion dam on there.

Where you should focus are on the features that are negative results of the manufacturing process, not those that were specifically engineered in. Casting lines, surface porosity (exhaust side), valve stem hump, etc.

The biggest thing for someone starting off porting is to do the same thing on all cylinders. Port x feature and then repeat it six times before moving on to port another feature. Last thing you want is cylinder to cylinder flows being all over the place.

 

I am with bumpin' on this. It's been a while, but I read a lot of discussions about the shape of the exhaust ports being important. But you are working with donor parts, if you are willing to tinker and possible rip the heads out multiple times, you could look into trying a few different things.

Something you might want to consider is an idea I got from the Bonneville group. Port (not gasket) matching the L36 lower intake to the heads. I did that, along with expanding the coolant bypass and an L26 water pump (has a cast impeller, better flow vs the stamped steel one GM used). You could also use a Series 1 3800 water pump, but you will also need the Series 1 pump pulley.
Here is what I did with my lower intake:
'04 Monte Carlo SS - Port Matched LIM

And here is my stock water pump to the L26 pump:
http://crzyz28.sytes.net/mycars/2004...mp_Upgrade.jpg

 

IMO the hard part about trying new stuff with head porting is figuring out if you were successful or not. Even the best heads dont gain a ton of power on their own on this platform, so gains ranging from say half that to losing a few % of hp is easily into the error range of the 'butt dyno'.

If I wanted to try some wild porting for the first time, I'd pick up a 3rd head from the junkyard. Hot tank it so its spotless. Leave 1 cylinder stock and then do 2 different port jobs on the other cylinders. Send it off to a shop to get flow benched and then compare the results to your cam profile. Then just replicate whichever port job worked the best on your 2 sets of real heads.

No doubt it would be expensive, youd probably have a few hundred wrapped up in it - but compared to $1500-2000 for full aftermarket units, you're still way ahead on price.

 

I have five heads in total. Two on the daily, two on the donor car, and one I pulled from the junkyard. I did experiment a little on the one I pulled from the junkyard a while back.
Is the theory behind port matching vs. gasket matching basically gasket matching yields minimal gains for the effort, while port matching isn't as intensive yet still yields gains?
As for the water pump, I want to switch to a Meziere electric pump

 

From what I've seen, I wouldn't put too much thought / effort into it either way. If you look at flow dynamics within a constrained space, like a tube or port, your highest flow / velocity is in the middle. At the wall, the velocity is very slow, even worse so in a rougher / more turbulent port like youd see on the intake side of the head. That flow / velocity increases gradually the further you get from the wall.

So I wouldn't put a ton of time into getting this area absolutely perfect at the interface between the two as it accounts for an incredibly small portion of your overall flow. I'd just pick a method and run with it.


In theory though, I do have a few concerns about gasket matching:
-The size / shape of that gasket port is generally not an extremely precise machined part (I imagine they're just cast or injection molded). As long as the manufacturer has the seal in the right spot and the gasket isnt grossly hanging into the port, that's good enough. I'd imagine if you lined up multiple brands of gaskets (or even the same brand over years of production) that this wouldn't be ultra consistent.

-As above, the bolt holes in the gasket likely also are not a precision machined surface and are oversized, allowing the gasket to 'float' a bit which would make porting exactly up to it kinda useless as you wouldn't have repeatability.

-My other concern is that you get a set of gaskets that's notably bigger for whatever reason (cheap knockoffs or something). As bigger isnt near the issue of too small, QC wont be as picky on that end of the spectrum. Gasket matching to that could create more work for you while trying to blend that larger size all the way into the intake plenum as you dont want the port to go small to big back to small.


Again, just theory / speculation on my part from a bit of engineering background.

 

Obviously all I have to add to this subject is theory as well. My take on the gasket floating when marking is not just slap the gasket on there with a couple bolts and sharpie any exposed metal. What I did when I practiced some porting a while ago, is I put the gasket in place with a few bolts, and move it to the right, then I'd mark the left side of the gasket. Do that for all the other directions, and you should have a gasket matched port, that isnt off center because of the botls, and should be less prone to having a gasket protruding into the runner. I like to take the time to do things people say aren't worth the time, to maximize efficiency where ever possible. For example, back in august I was having an issue with the car when I gave it throttle at low speed. It wouldn't respond at first, then would lurch forward. I thought the issue was the throttle sticking, so I took it off and cleaned all the carbon off the back side of the plate. After cleaning it, I also polished the throttle body.









Here's the video I've gotten most of my knowledge on port/polishing from:

 

Bumpin' gave a lot of good info about the gasket vs port matching. Simple sum up from my seat, the port matching the LIM to the heads is to just get a more continuous flow. Gasket matching, in addition to what Bumpin' said about how different gasket manufacturers may over size the ports and such, is if you don't have the correct measuring tools, trying to ensure that a port that large is continuous through the head, other wise, it could have been a lot of effort for nothing. Also, checking the thickness of the various parts of the head before you break through OR compromise it. some how.

As for the throttle body, I have been pretty please with switching my upper intake to a L26 aluminum one and using a L67 throttle body (which I modded both items, there are thread on MCF about those adventures).

 

I get wanting to make everything perfect, but my point is that theres got to be some balance there or the project will never get done chasing the last tenth of a percent.

In terms of the heads, what I mean is that the inlet of the intake is the nicest part of the whole port since it's such a simple casting up there. The real gains are to be had down inside in the bowl area, which is why the aftermarket ported heads focus so much on that area.

Heads aren't going to gain a ton of power anyways, so you may as well spend the free time you have on getting the big hitters knocked out.


One other thing to mention relative to 3800 head porting. Before you put any work into it, I'd clean it up and pull the valves and take a very close look between the valves to make sure it's not cracked.